• “Why don’t I have abs yet?” (Because you have a day job, enjoy Doritos, and aren’t a genetic freak.)

But when the questions get really tough, I turn to Adam Campbell, the Men’s Health Fitness Director. He sits right next to me. Adam understands fitness better than anyone I know.

In fact, a few years ago, I walked into his office and told him that I was hiring a personal trainer. Even though I was exercising—pushups, situps, crunches—I was still packing on pounds. That morning, I’d looked in the mirror and saw a fat guy staring back. I freaked. I needed to make big changes, quick.

An hour? Adam promised that if I could make time to exercise 20 minutes a day, three days a week—while cutting my two-sodas-a-day habit—I’d be lean again in no time. My workouts were ineffective, he explained, because I was battering the same small muscles over and over. He gave me a workout that hit all my large muscle groups. When these muscles grew bigger, he said, they’d burn more calories—and I’d begin to lose weight.

He was right. Over the next six months, I dropped 20 pounds.

If you’ve looked into the mirror recently and didn’t recognize the person staring back, I’ve got good news. Adam is happy to be your personal trainer, too. I asked him what advice he’d give men and women in my situation: Working out, but not seeing results. He wrote up this list of the five biggest fitness blunders—along with the fixes you need for the results you want.

Mistake #1: You Don’t Lift Weights
You’ve no doubt been told that aerobic exercise is the key to losing your gut, but weight training is actually more valuable. Three reasons:

1. Lifting protects your muscle. When people diet without lifting weights, research shows that 75 percent of their weight loss is from fat and 25 percent is muscle. That 25 percent may reduce your scale weight, but it doesn’t do a lot for your reflection in the mirror. However, if you weight train as you diet, your weight loss is more likely to be 100 percent fat. Think of it in terms of liposuction: The whole point is to simply remove unattractive flab, right? That’s exactly what you should demand from your workout.

2. Lifting boosts your metabolism. Your muscles need energy to repair and upgrade your muscle fibers after each resistance-training workout. For instance, a University of Wisconsin study found that when people performed a total-body workout comprised of just three big-muscle exercises, their metabolisms were elevated for 39 hours afterward. What’s more, they also burned a greater percentage of their calories from fat during this time, compared with those who weren’t hitting the weights.

3. Lifting torches calories. It’s considered common knowledge that jogging burns more calories than weight training. Turns out, when scientists at the University of Southern Maine used an advanced method to estimate energy expenditure during exercise, they found that weight training burns as many as 71 percent more calories than originally thought. The researchers calculated that performing just one circuit of eight exercises—which takes about 8 minutes—can expend 159 to 231 calories. That’s about the same as running at a 6-minute mile pace for the same duration.

Need a weight workout? No matter your goal, we have the right workout for you.

Mistake #2: You Don’t Use the Right Dumbbells
Ladies, we’re especially talking to you on this one. Your goal is to challenge your muscles, not just go through the motions. For instance, if you can lift a weight 15 times, it’s not going to do your muscles much good to lift it for only 8 repetitions. A good way to gauge if a weight is appropriate: Note the point at which you start to struggle. Let’s say you’re doing 10 repetitions. If all 10 seem easy, then the weight you’re using is too light. However, if you start to struggle on your tenth repetition, you’ve chosen the correct poundage.

Mistake #3: You Don’t Work Your Lower Body
To cut inches from your waist, make sure you’re working the muscles below your belt. In a Syracuse University study, people burned more calories the day after they did lower-body resistance training than the day after they worked their upper body. “Leg muscles—like your quads and glutes—generally have more muscle mass than those of your chest and arms,” says study author Kyle Hackney, Ph.D. (c), C.S.C.S. “Work more muscle during your exercise session, and your body has to expend more energy to repair and upgrade them later.” So the best approach, of course, is to hit every muscle each workout.

Mistake #4: You Don’t Watch What You Eat
You can’t out-exercise a bad diet. After all, you can eat 1,000-calorie fast food burger in just 5 minutes, but it’ll take you more than an hour to burn that many calories with physical activity. So make sure you’re not using exercise as an excuse to eat whatever you want. You may even find that regular workouts help you better follow a smart eating plan. Case in point: University of Pittsburgh researchers studied 169 overweight adults for 2 years and found that the participants who didn’t follow a 3-hour-a-week training plan ate more than their allotted 1,500 calories a day. The reverse was also true—sneaking snacks sabotaged their workouts. The study authors say it’s likely that both actions are a reminder to stay on track, reinforcing your weight-loss goal and drive.

Mistake #5: You Skip Workouts
We’re all busy, but that’s usually just a lame excuse. After all, plenty of people find time to exercise. And when was the last time you heard someone say they regretted their workout? Probably never, and here’s why: U.K. researchers found that workers were 15 percent more productive on the days they made time to exercise compared to days they skipped their workout. They were also 15 percent more tolerant of their coworkers. Now, consider for a moment what these numbers mean to you: On days you exercise, you can—theoretically at least—accomplish in an eight-hour day what normally would take you nine hours and 12 minutes. Or you’d still work nine hours, but get more done, leaving you feeling less stressed and happier with your job, another perk that the workers reported on the days they exercised.